1. Field of the Invention
This invention relates to a silicon semiconductor device and a method for manufacturing the same, particularly to an insulating isolation groove between electronic elements and a method for manufacturing the same.
2. Description of the Prior Art
In the past, an isolation of the element by the groove of this kind has been performed by embedding a polycrystal silicon film 6b within a groove and oxidizing the top surface of the polycrystal silicon film 6b to form an insulating film such as a silicon oxide film 9, as shown in FIG. 1 (c), or by embedding an insulating film such as a boron phosphosilicate glass film 8 or the like within a groove as shown in FIG. 2 (c).
FIGS. 1 (a)-(c) show a sectional view illustrating in order each step of a prior process for forming an isolation groove by embedding a polycrystal silicon film within a groove. FIG. 1 (a) shows a product formed by forming in order a silicon oxide film 2 and a silicon nitride film 3 on the top surface of a silicon wafer substrate 1, making an opening selectively in the silicon nitride film 3 and the silicon oxide film 2 by a photoetching method, then forming a groove having a depth of 3-5 .mu.m in the silicon substrate 1 exposed in the opening by an anisotropic etching method, forming a silicon oxide film 4 having a thickness of 1000.ANG. on the inner surface of the groove by using the silicon nitride film 3 as a non-oxidizable mask and allowing a polycrystal silicon film 6 to grow by a low pressure CVD method till the surface thereof practically becomes flat. Then, as shown in FIG. 1 (b), the polycrystal silicon film 6 is etched back so as to make the surface of the polycrystal silicon film 6 consistent with the surface of the silicon substrate 1. Thereafter, as shown in FIG. 1 (c), the resulting polycrystal silicon film 6b is oxidized using the silicon nitride film 3 as a mask to form a silicon oxide film 9 and the silicon nitride film 3 is removed to form an isolation groove.
FIGS. 2 (a)-(c) show each step of the prior second process for manufacturing an isolation groove. FIG. 2 (a) shows steps which comprise a product formed by forming a groove and forming a silicon oxide film 4 on the inner surface of the groove as shown in FIG. 1 (a), and thereafter removing a silicon nitride film 3, forming a silicon nitride film 5 and embedding a boron phosphosilicate glass film 7 within the groove. Then, as shown in FIG. 2 (b), a thermal treatment is carried out to allow a boron phosphosilicate glass film 7b to reflow. Thereafter, as shown in FIG. 2 (c), the boron phosphosilicate glass film 7b is etched back to make the surface of the resulting boron phosphosilicate glass film 7c consistent with the surface of the silicon substrate 1, and then a silicon oxide film 8 is built up to form an isolation groove.
The prior isolation groove as mentioned above, in case of the construction wherein the polycrystal silicon film 6b is embedded within the groove as shown in FIG. 1 (c), brings about an increase in capacitance between electronic elements as compared with that of the construction having the embedded insulating film and thus is an obstacle to a speeding-up of the element. In addition, since the surface of the polycrystal silicon film 6b is oxidized when the groove is formed, a crystal defect occurs in a region of the element and thus a problem is raised in the element characteristics. Moreover, the thickness of the silicon oxide film 9 decreases at the end of the sidewall of the groove as shown in a circle indicated with an arrow in FIG. 1 (c). Therefore, there is a defect that in the case that when a hole leading to the element region is provided, if an allowance between the hole and the groove is reduced, a hole is formed also on the polycrystal silicon film within the groove, whereby a problem such as a short-circuit between the elements or the like is raised. In the case that the insulating film 7c such as a boron phosphosilicate glass film of the like is embedded within the groove as shown in FIG. 2 (c), a problem of a deformation is raised due to the difference in coefficient of thermal expansion between the silicon of the element region and the insulating film. In addition, there is a defect that the short-circuit due to an aluminum residue occurs in the subsequent processing step, since a "void" occurs within the boron phosphosilicate glass film in the embedding step as shown in FIG. 2 (a) and as a result, a difference in level occurs on the top surface of the groove after reflowing.